Procedure for manufacture of lithium grease



United States Patent PROCEDURE FOR MANUFACTURE OF LITHIUM GREASE No Drawing. Application August 30, 1954 Serial No. 453,118

Claims. (Cl. 252-41) This invention relates to an improved process for the preparation of grease compositions and more particularly to an improved process for the preparation of smooth-textured lithium base greases.

The addition of a lithium compound such as the lithium soap of a higher fatty acid, for example, lithium stearate, lithium hydroxy stearate, lithium pahnitate, lithium oleate, and the like, to a mineral oil produces grease compositions having properties that are widely different from other alkali metal soap-type greases. Since lithium base greases possess a high melting point, they can be employed as lubricants over a wide temperature range, and being water resistant they are substantially unaffected by the solubil-izing or leaching effect of water.

We have found that an improved grease composition having a smooth texture can be obtained from a lithium soap and an oil by a process which comprises heating a mixture comprising a fatty material, a lithium compound capable of saponifying therewith, an oil and water in a closed container until an elevated pressure is reached, venting the vapors formed therein from said container beginning at said pressure and progressively reducing the pressure therein While continuing to heat the same, continuing such heating until the contents of said container are substantially simultaneously at a temperature high enough to melt the lithium soap and about atmospheric pressure, and thereafter adding to the resulting mixture obtained additional oil to produce the desired grade of grease.

The preparation of grease in accordance with the process of this invention offers several distinct and important advantages. Saponification at high temperatures in the presence of water vapor under pressure in accordance with this invention assures completion of saponification and dehydration in the substantial absence of air, thereby preventing the oxidation of the organic constituents and the formation of charred particles. Operation in the presence of water at higher temperatures and under pressure, rather than at lower temperatures in the presence of Water in an open container, speeds the saponification reaction and the entire grease preparation and results in a substantial decrease in overall process time. In the preparation of the lithium base grease in accordance with the present process water is employed to bring about the saponification reaction and to effect better dispersion of the lithium soap in the oil. Since the reaction is conducted under pressure in a closed container for a portion of the time, the amount of water necessary for the reaction is substantially reduced over that required in an open container and the dehydration period is correspondingly shortened. By reducing the amount of water, moreover, the excessive foaming that would likely follow from the use of a large amount of water is substantially reduced. By operating in a closed container until a certain defined temperature is reached, venting and continuing heating until the final temperature is obtained, the entire saponi-fication reaction can be carried out in the same container and in a relatively short 2,847,382 Patented Aug. 12, 1958 2 4 time. When the final temperature is reached, dehydration is substantially complete and the remainder of the oil can then be added to the reaction mixture immediately, further cuttingdown on process time. In addition, by carrying out the present process in a closed container under the pressure and temperature conditionsrecited herein, We are able to'eifect eflicient dispersion of the lithium soap into the oil without any resulting graininess or undesirable lumps that would have to be removed by careful milling.

The oil which is employed in the present process in combination with the lithium soap can be a mineral oil, a synthetic oil or an organic oily medium, depending upon the composition of the grease desired. Thus, a mineral oil having a viscosity above about seconds SUV at 100 F., and preferably about 1100 to about 1500 seconds SUV at 100 F., can be used. If desired, a blendof oils of suitable viscosity can be employed instead of a single oil. The oil content of the greases prepared according to the present invention can be varied over a wide range, although a range of about 75 to about 97 percent by weight of the final grease composition is preferred. The particularoil, as Well as the amount of oil employed, depends, of course, upon the characteristics desired in the final grease composition.

The lithium soap employed in the present invention can be prepared from fats or the higher fatty .acids, such as stearic, hydroxy stearic, palmitic, oleic, andthe like. The lithium compounds are the true soaps or salt which are formed by the replacement of the hydrogen atom of the carboxyl group or groups of the acid. In place of the substantially pure fats or acids, we can .use mixtures of fats or fatty acids such as those obtained from the various fatty oils such as cotton seed oil, rapeseed oil, animal oils, fish oils, and the like. The saturated fatty acids such as those derived-from hydrogenated 'oils of vegetable, animal and marine extraction can also be used. For example, we can prepare the lithium soap of the fatty acids obtained by the hydrogenation of a fish .011, such as sardine oil, herring oil, cod oil, menhaden oil, and the like. The hydrogenation of these oils is not a part of this invention but can be carried out by various known processes such, for example, as the process described on pages 372 to 430 of Hydrogenation of Organic Substances, 3rd edition, by Carleton Ellis, D. Van Nostrand Co., Inc., New York (1930). The amount of the lithium soap employed should be sufficient to thicken the oil to the consistency of a grease and can vary from about 3 to about 25 percent by weight of the final I saponification in accordance with the present invention grease composition. Thus, for greases of the type employed in the lubrication of automobile chassis and wheel bearings, the lithium soap content of the grease can-compriselabout 5 to about 15 percent by weight of the grease composition.

As noted above, the amount of water necessary to effect is relatively small and is substantially reduced by op eration in accordance with the reaction conditions herein. set forth. The amount necessary is that needed to bring about the'saponification reaction 'and'eifect dispersion of the lithium soap in the oil. We have found that about 0.6 to about 3.0, preferably about 0.7 to about 1.0, per-j cent'by weight of Water, based upon the total original charge in the container, is necessary to obtain thedesired results of this invention. I

'When desired we can add an-antioxidant to the greasecompositions of the present invention. Thus, in in-- stances where the grease compositions herein prepared are to be subjected to prolonged use under oxidizing conditions, we can advantageously incorporate therein "a small amount of a 'diaryl amine oxidation inhibitor. As

examples of some of the diaryl amines which can be used in the preparation of the lithium base greases in accordance with the process described herein may be mentioned diphenylamine, phenyl alpha naphthylarnine, phenyl beta naphthylamine, alpha alpha-, alpha beta-, and beta betadinaphthylamines and the like. The amount of the diaryl amine employed will depend to a large extent upon the severity of the conditions to which the grease is subjected, as well as the particular diaryl amine used. Generally, however, the amount of diaryl amine employed is between about 0.1 and about 1.5 percent by weight based upon the weight of final total lithium grease composition.

A preferred embodiment for the preparation of lithium base greases in accordance with the present invention can b e described in the following manner:

The saponification charge comprising a lithium compound, such as lithium hydroxide, fats and/ or fatty acids and water, and a relatively small amount of a mineral oil.

is placed in a jacketed kettle equipped with a stirrer, after which the kettle is closed and heat obtained from any suitable source is applied thereto. Heating of the contents of the kettle is continued until the internal pressure thereof is about 30 to about 90 pounds per square inch gauge, preferably about 50 to 70 pounds per square inch gauge. While pressures lower than 30 pounds per square inch can be used, the pressure should be high enough to obtain sufficiently high temperatures to complete saponification of the charge in a reasonable amount of time. Pressures in excess of 90 pounds per square inch can be used provided the equipment employed can withstand such pressures. Generally the amount of time required to obtain the required pressure upon application of heat to the kettle is about 20 to about 45 minutes.

When the above pressure is reached venting of the vapors (substantially water vapor) from the kettle is begun and the pressure therein is progressively reduced.

The application of heat to the contents of the kettle is continuously maintained thereon, however, and this is continued until substantially simultaneously the temperature of the contents of the kettle is about 360 to about 420 F., preferably about 390 to about 400 F., and the internal pressure is about atmospheric. The final temperature can be varied from that set forth above, but in any event it must be high enough to melt the lithium soap but not so high that degradation or decomposition of the contents of the kettle will result. The time interval which elapses from the time venting of the vapors from the kettle begins to the time atmospheric pressure and the desired elevated temperature is reached will depend on many variables of course, but in general. a period of about one to two hours is usually suificient.

Dehydration of the contents of the kettle begins the moment venting is started. Under the reaction conditions herein set forth for preparing lithium base greases, dehydration of the contents of the kettle is substantially complete when atmospheric pressure and the desired elevated temperature are reached. To insure and/ or hasten complete dehydration a vacuum can be applied to the kettle when atmospheric pressure is reached therein. A vacuum of 20 inches of mercury applied for five minutes has been found to be sufficient.

To the resulting mixture at atmospheric pressure and the temperature at which it may be when dehydration is complete, for example, about 360 to about 420 F., is added additional oil such as a petroleum oil, of a temperature and in an amount such as not to obtain a mixture difficult to stir. The same or different oils are continued to be added to the resulting grease mixture until a grease of desired consistency is obtained. The oil which is added to the saponification mixture is somewhat cooler than said mixture and consequently the resulting grease is at a somewhat lower temperature. If desired the grease can be milled, but this is generally not necessary. The grease 4 prepared can then be packaged or can be further treated to satisfy individual requirements.

As a specific example of operation in accordance with our invention, a charge comprising 8080 pounds of 500/ 3 Texas oil (a naphthenic-type oil having about 500 viscosity SUV at 100 F.), 260 pounds of beef tallow, 2300 pounds of hydrogenated castor oil, 355 pounds of lithium hydroxide monohydrate and 76 pounds of water was placed in a container provided with a stirrer. The container was then closed, after which heat was applied thereto through indirect contact with a petroleum oil at a temperature of about 450 F The contents of the container were stirred continuously during this period and heating thereof was continued for about 30 minutes until an internal pressure of about 65 pounds per square inch gauge was reached.

When the pressure of 65 pounds per "quare inch was reached, venting of the vapors from the container was begun and heating was continued for about one and onehal-f hours until a temperature of about 395 F. and atmospheric pressure was reached. Dehydration of the resulting grease mixture was substantially complete at this point, but to insure complete dehydration a vacuum of 20 inches of mercury was applied thereto for about five minutes.

To the dehydrated grease mixture with stirring was added 3570 pounds of 500/3 Texas oil of about room temperature. The temperature of the mixture after such addition was about 325 F. The mixture was then transferred to a water-jacketed kettle, after which cooling water was passed through the jacket and 10,750 pounds of 150 Mid Continent Bright Stock at room temperature was added to the mixture until the soap content was about 10 percent by weight. The temperature of the resulting grease was about 225 F. The grease obtained was tested in accordance with ASTM D217-52T, and, after strokes, was found to have a penetration test of 245. The grease did not require milling and had a smooth, buttery texture.

Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A method of preparing a lithium base grease which comprises heating a mixture comprising a fatty material, a lithium compound capable of saponifying therewith, an oil and about 0.6 to about 3.0 percent by Weight of water in a closed container until a pressure of about 30 to about 90 pounds per square inch is reached, venting the vapors formed therein from said container beginning at said pressure and progressively reducing the pressure therein while continuing to heat the same, continuing such heating until the contents of said container are substantially simultaneously at a temperature of about 360 7 to about 420 F. and about atmospheric pressure, and

thereafter adding to the resulting mixture obtained additional oil to produce the desired grade of grease.

2. A method of preparing a lithium base grease which comprises heating a mixture comprising a fatty material, a lithium compound capable of saponifying therewith, an oil and about 0.6 to about 3.0 percent by weight of water in a closed container until a pressure of about 50 to about 70 pounds per square inch is reached, venting the vapors formed therein from said container beginning at said pressure and progressively reducing 'the pressure therein while continuing to heat the same, continuing such heating until the contents of said container are substantially simultaneously at a temperature of about 390 to about 400 F. and about atmospheric pressure, and thereafter adding to the resulting mixture obtained additional oil to produce the desired grade of grease.

3. A method of preparing a lithium base grease which comprises heating a mixture comprising a fatty material, a lithium compound capable of saponifying therewith, an oil and about 0.7 to about 1.0 percent by weight of water, based upon said mixture, in a closed container until a pressure of about 50 to about 70 pounds per square inch is reached, venting the vapors formed therein from said container beginning at said pressure and progressively reducing the pressure therein while continuing to heat the same, continuing such heating until the contents of said container are substantially simultaneously at a temperature of about 390 to about 400 F. and about atmospheric pressure, and thereafter adding to the resulting mixture obtained additional oil to produce the desired grade of grease.

4. A method of preparing a lithium base grease which comprises heating a mixture comprising lithium hydroxide monohydrate, beef tallow, hydrogenated castor oil, oil and about 0.6 to about 3.0 percent by weight of water, based upon said mixture, in a closed container until a pressure of about 30 to about 90 pounds per square inch is reached, venting the vapors formed therein from said container beginning at said pressure and progressively reducing the pressure therein while continuing to heat the same, continuing such heating until the contents of said container are substantially simultaneously at a temperature of about 360 to about 420 F. and about atmos- 6 pheric pressure, and thereafter adding to the resulting mixture obtained additional oil to produce the desired grade of grease.

5. A method of preparing a lithium base grease which comprises heating a mixture comprising lithium hydroxide monohydrate, beef tallow, hydrogenated castor oil, oil and about 0.7 to about 1.0 percent by weight of water, based upon said mixture, in a closed container until a pressure of about to about pounds per square inch is reached, venting the vapors formed therein from said container beginning at said pressure and progressively reducing the pressure therein while continuing to heat the same, continuing such heating until the contents of said container are substantially simultaneously at a temperature of about 390 to about 400 F. and about atmospheric pressure, and thereafter adding to the resulting mixture obtained additional oil to produce the desired grade of grease.

References Cited in the file of this patent UNITED STATES PATENTS 1,912,001 Lauer May 30, 1933 2,397,956 Fraser Apr. 9, 1946 2,697,693 Browning et al. Dec. 21, 1954 

1. A METHOD OF PREPARING A LITHIUM BASE GREASE WHICH COMPRISES HEATING A MIXTURE COMPRISING A FATTY MATERIAL, A LITHIUM COMPOUND CAPABLE OF SAPONIFYING THEREWITH, AN OIL AND ABOUT 0.6 TO ABOUT 3.0 PERCENT BY WEIGHT OF WATER IN A CLOSED CONTAINER UNTIL A PRESSURE OF ABOUT 30 TO ABOUT 90 POUNDS PER SQUARE INCH IS REACHED, VENTING THE VAPORS FORMED THEREIN FROM SAID CONTAINER BEGINNING AT SAID PRESSURE AND PROGRESSIVELY REDUCING THE PRESSURE THEREIN WHILE CONTINUING TO HEAT THE SAME, CONTINUING SUCH HEATING UNTIL THE CONTENTS OF SAID CONTAINER ARE SUBSTANTIALLY SIMULTANEOUSLY AT A TEMPERATURE OF ABOUT 360* TO ABOUT 420*F. AND ABOUT ATMOSPHERIC PRESSURE, AND THEREAFTER ADDING TO THE RESULTING MIXTURE OBTAINED ADDITIONAL OIL TO PRODUCE THE DESIRED GRADE OF GREASE. 